1. Field of the Invention
The present invention relates to a force detection device for detecting an operation force of an operator applied in a uniaxial direction.
2. Description of Related Art
There has been conventionally proposed a truck having a power assist function for assisting human power with motive power. FIG. 10 shows a conventional power-assisted truck 8. The power-assisted truck 8 has a holding part 84 provided with a handle 80 to be given an operation force by an operator. A pair of force detection devices 9, 9 are disposed at both ends of the handle 80 (see JP 9-202235 A, for example).
The holding part 84 is supported on a base holding part 85 via four posts 83-83. Disposed on the base holding part 85 are two motors 82, 82, drive control devices 86 for controlling rotation of the motors 82, and batteries 87 for supplying power to the motors 82. Both motors 82, 82 are coupled to a pair of wheels 81, 81.
FIG. 11 shows a force detection device 9. A hinge 94 is placed on an upper portion of the post 83. The handle 80 is coupled to the hinge 94 at a base end thereof. A load cell 93 including a pressure sensor is disposed above the hinge 94. The load cell 93 has one end thereof attached to the handle 80, and the other end attached to the post 83.
A handle locking part 90 projects from the post 83 above the load cell 93. The handle locking part 90 is provided with a handle locking hole 91 in the form of a long hole. The handle 80 penetrates the handle locking hole 91. A spring 92 is stretched between the handle 80 and the post 83 above the handle locking part 90. The spring 92 applies a preload to the load cell 93.
When an operator applies an operation force to the handle 80, the handle 80 swings on the hinge 94. When the operation force is loosened, the handle 80 returns to a position right above the hinge 94 due to an elastic repulsive force of the spring 92. The operation force applied to the handle 80 by the operator can be found from a difference between a detected value of each load cell 93 and the preload. The drive control devices 86 are controlled depending on a magnitude of the force.
With the force detection device 9, when the operator applies a force forward to the handle 80 with the handle 80 slightly inclining, because the handle 80 may swing on the hinge 94, the load cell 93 will receive a horizontal component and vertical component of the force, and detect the horizontal component. Although the load cell 93, which is a pressure sensor, is intended to detect only a uniaxial force, the load cell 93 indeed receives not only the uniaxial force but also a force perpendicular thereto, as described above. This has been preventing the horizontal component from being detected with high accuracy.